1. Technical Field
This invention relates generally to hot gas control systems such as those utilized, e.g., in some flight control systems and the like. It concerns a hot gas control system and associated methodology that allow use of a wider range of propellant formulations by reducing contamination otherwise caused by condensible and magnetic species in the gas stream.
2. Background Information
The hot gas utilized in a hot gas control system is sometimes produced in a solid propellant gas generator that includes a pressure vessel in which is disposed a suitable solid propellant or grain. Once the propellant is ignited, hot gas flows from the vessel along a ducting path, defined by suitable ducting structure, as the hot gas is utilized in performing some function, such as controlling various guidance components. The ducting path may include very narrow passages and small orifices on the order of less than a millimeter in diameter, and so it is important to consider contaminants in the hot gas that can accumulate in the ducting path, reduce performance,,and cause malfunctioning.
One contaminant of particular interest includes condensible species such as hydrochloric acid. Another contaminant includes various ferrocenes, i.e. materials having notable magnetic properties. Both contaminants are initially of no concern as the hot gas leaves the vessel because the condensible species are in a gaseous state and the temperature of the ferrocenes is typically above the Curie temperature so that their magnetic properties are nil. However, both contaminants can cause severe problems if they are cooled as they pass along the unheated ducting path.
As the ducting structure is (at least initially) at a significantly lower temperature than the hot gas, heat is withdrawn from the gas stream, which can result in the condensible species being transformed to the liquid or solid state and the ferrocenes becoming magnetic as they drop below their Curie temperature. Such events can result in system clogging, and thus lead to system failure or reduction in performance. The deleterious effect essence of magnetic particles is further aggravated when the control system is of the type which employs magnetic drivers.
Thus, these contaminants must be avoided when choosing the propellant to be used, which significantly limits the number of available propellant choices. Generally, the propellant must be such as to produce a "clean" gas in the sense that the level of contaminants is low enough that the risk of blockage is acceptably low, i.e. the level is virtually nil in practice. When this requirement is combined with the desire for high energy content, burning rate and pressure relationships, temperature, and density, the choices of propellant candidates are severely restricted.
Consequently, if a method or technique could be devised that permits use of propellants which have improved operational properties but contain condensible and/or magnetic constituents, system design and performance advantages could be realized.
Prior art in this field includes U.S. Pat. No. 3,147,710 to Gluckstein which relates to solid propellant compositions and to a method of igniting solid propellant rocket motors.
U.S. Pat. Nos. 3,165,060 and 3,217,651 to Braun, et al. describe multiple propellent grain for rocket motors, and U.S. Pat. No. 3,427,805 to Osburn describes a combustion barrier embedded within the grain for varying the burning pattern.
U.S. Pat. No. 3,668,872 to Camp, et al. describes a method and apparatus for utilizing the volatility of the combustion products of solid metallic propellants to accelerate metal combustion products to gaseous velocity by recondensing the gaseous products in the rocket envelope behind the throat of the nozzle.
U.S. Pat. No. 4,466,352 to Dalet, et al. describes a propellant that burns in at least two thrust modes, one providing an acceleration phase and the other a cruising phase.
U.S. Pat. No. 4,574,700 to Lewis describes a solid propellant grain having a main portion and a nozzle portion. The nozzle portion is a shaped and cured propellant having a lower burn rate and a plurality of aromatic amide fibers dispersed therethrough.
U.S. Pat. No. 4,594,945 to Alexandris describes a thermal protection for propellant grains, and U.S. Pat. No. 4,627,352 to Brachert, et al. describes a multi-base powder charge for propellants. Thus, none of these patents addresses a solution to a problem that is unique to warm or hot gas pneumatic control systems of the type described.